1. Field of the Invention
This invention relates generally to medical electrode systems and, in particular, to a defibrillator electrode system for use with an automatic or semi-automatic external defibrillator (referred to collectively as "AEDs").
2. Description of the Prior Art
One frequent consequence of heart attacks is the development of cardiac arrest associated with heart arrhythmias, such as ventricular fibrillation ("VF"). VF is caused by an abnormal and very fast electrical activity in the heart. During VF the heart cannot pump blood effectively. VF may be treated by applying an electric shock to the patient's heart through the use of a defibrillator. Defibrillation clears the heart of the abnormal electrical activity by depolarizing a critical mass of myocardial cells to allow spontaneous organized myocardial depolarization to resume, thus restoring normal function. Because blood no longer pumps effectively during VF, the chance of surviving cardiac arrest decreases with time after the arrest. Quick response to cardiac arrest by administering a defibrillating shock as soon as possible after the onset of VF is therefore often critically important.
Increasing the number of potential defibrillator operators who are trained in the proper use of an AED increases the likelihood that a trained defibrillator operator will be available during an emergency and thus could ultimately reduce the defibrillator deployment time. As the number of potential operators increases, however, the frequency with which each operator uses the skills developed during training decreases. Depending upon the amount of time since the defibrillator operator last used a defibrillator, review of electrode placement instructions will likely be required to determine correct placement of the electrode pads. Failure to apply the electrode pads correctly can reduce the amount of defibrillation energy that is applied to the myocardium. Misapplied electrodes can allow the current to flow along the chest wall, thus missing the heart, and result in a failure of the defibrillation shock. Such a review of pad placement, while necessary, delays the speed with which defibrillation can be performed on the patient. With every second that passes, the likelihood of successfully restoring the patient's heart to a normal sinus rhythm decreases. Therefore, every step in the deployment and use of a defibrillator that can be streamlined is critical.
One time saving gain has been the development of electrode pads which eliminate the step of attaching electrode pads to the cable, and, for the most part, eliminate the need to untangle the cable. An example of such an electrode system is described in U.S. Pat. No. 5,466,244 for "Defibrillator Electrode System" by Morgan. Other electrode pad designs are known in the art.
An additional concern relates to the whether the rescuer, or any other person touching the patient during shock delivery, is at risk of being shocked. It is possible, that a voltage gradient of sufficient magnitude could be generated which could shock a rescuer. In some situations such a voltage gradient could appear within 5 cm of the perimeter of a standard electrode.
Currently available defibrillator electrode pads used with AEDs use two adhesive electrode pads with an insulated backing. The two adhesive pads reduce the risk that the rescuer will be shocked by eliminating the need for direct contact with the electrodes during shock delivery. Hospital defibrillator electrodes, on the other hand, require the operator to hold the electrode paddles to the patient's chest when delivering the shock. In spite of the fact that the rescuer typically is not in contact with the patient when delivering a shock through the adhesive electrodes, there is still a concern that the area between the electrodes where the current flows could, nonetheless, increase the rescuer's shock risk.
Another problem relating to adhesive electrodes relates to proper placement. Whether electrodes are used for defibrillation, monitoring, or pacing, proper placement of the electrodes is important for collecting and assessing the most accurate patient data. For example, when defibrillator electrodes are not properly placed on the torso, the shock delivered through the heart does not travel directly through the heart and the shock is less efficacious.
Another difficulty that is encountered relates to administration of cardiopulmonary resuscitation ("CPR") in connection with defibrillation. When a lay user (e.g. police officer, fire fighter, airline attendant, or security guard) is operating a defibrillator they may be out-of-practice with the location for CPR compression (for cardiac compression). Additionally, there is currently no method for determining whether the rescuer is pressing hard enough to pump blood for the victim. CPR without correct compression, in both placement and pressure, does not effectively pump the victim's blood.
What is needed is an easy to use electrode system that reduces the risk of incidental shock to the rescuer or a bystander. What is also needed is an electrode system that shows the rescuer where to administer the CPR compressions. Additionally what is needed is an electrode system that provides life size markers for correct electrode pad placement, or additional instructions for AED usage or CPR administration. Also what is needed is an electrode system that provides additional circuitry for detecting CPR rate and force, allowing the defibrillator to use the information to provide feedback to the rescuer.